This invention relates to an industrial machine control device for controlling machine tools and other industrial machines, and more particularly to an industrial machine control device in which a first control unit, namely, a numerical control device applies mechanical coordinate data to a second control unit, namely, a programmable controller at all times, and the programmable controller monitors the mechanical coordinate data, thereby to perform a sequence operation as required.
FIG. 1 is a block diagram showing the arrangement of a conventional industrial machine control device, namely, a numerical control device thereinafter referred to as "an NC device", when applicable). FIG. 2 is an explanatory diagram showing a machine to be controlled by the device.
In FIG. 1, reference numeral 1 designates a memory made up of a RAM for storing programs and data; 2, a control section essentially comprising a CPU 2a, the control section operating to control the functions of the NC device according to the system software loaded therein; 3, an arithmetic section for performing numerical arithmetic operation under the control of the control section; 4, a tape reader for reading data from a paper tape in which an NC machining program (hereinafter referred to merely as "a machining program", when applicable) has been recorded by punching; 5, a program interface; 6, a drive section including a servo amplifier etc.; 7, a motor for driving a machine to be controlled (hereinafter referred to merely as "a machine:, when applicable); 8, an encoder for outputting a feedback signal; and 9, an input/output interface provided for input signals necessary for starting and stopping the NC device, and output signals such as NC device state signals, and auxiliary function signals for allowing the NC device to control external equipment. The machining program may be recorded on a floppy disc or the like instead of the paper tape.
In FIG. 2, reference numeral 20 designates a speed reducer; 21, a drive mechanism such as a ball screw; 22, a movable table of the machine, which is a tool mounting stand in the case of a lathe; and 23a, 23b, 23c and 23d, limit switches mounted on a stationary part of the machine, for outputting signals representing the current position of the movable table 22, i.e., the arrival of the machine at predetermined positions (hereinafter referred to as "predetermined position arrival signals", when applicable).
Under the control of the NC device 10, the machine operates to machine a workpiece (not shown). The above-described predetermined position arrival signals are applied, for instance, to a programmable controller (not shown, and hereinafter referred to merely as "a PC", when applicable). Before a workpiece is machined, the preparatory operation of a workpiece conveying device (not shown) is carried out, so that a workpiece machined is conveyed out of the machine without delay, according to the control operation of the programmable controller. The predetermined position arrival signals are used not only for achieving the preparatory operation of the workpiece conveying device, but also for performing sequence operations when the movable table reaches the predetermined positions.
With the above described conventional NC device, some detectors such as limit switches are provided at the predetermined positions to output the predetermined position arrival signals. The detectors are relatively short in service life. Therefore, the employment of the NC device is low in reliability and not so economical.
On the other hand, recently the following machining method has been extensively employed. Various kinds of workpieces are run on a single machining line, and the machine automatically changes the tool in correspondence to a workpiece coming in, so that a variety of workpieces are machined on one and the same machining line.
With such a machining line, sometimes all of the workpieces may be different in size or in configuration. It is necessary to change (according to a workpiece to be machined) the position where, upon arrival of the movable table, the preparatory operation of the workpiece conveying device should be started; that is, the machine's predetermined position.
For this purpose, with the conventional NC device, the positions of the limit switches must be changed resulting in some difficulty.